Can terra cotta balls be substituted for hydrotons?

hem_krishJune 19, 2009

In hydroculture, can I use terracotta balls instead of hydrotons? Clay pellets are very hard to find, here in India but I know this guy who attaches terracotta balls the size of marbles to pots to give them an enthnic look. I'm wondering if it will be worthwhile to commission these balls to use in hydroculture. I dont think the balls will be as porous, but will the spaces between the balls not be enough aeration?

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I don't see why not, but you will have to water them more frequently. Since they are "less porous", they will not hold water as long as hydroton.

    Bookmark   June 19, 2009 at 1:09PM
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Such clay balls are produced here in Thailand by some non profit organisations. The actuall disadvantage compared to EXPANDED clay is their weight. Porosity and other aspects depend on composition and fiering temperatures. I am actually a professional potter and was thinking of cheap additives and use of low-tech techniques to make the clay lighter. I haven't explored the topic so far because energy is expensive and I have kinda bigger fish, or let's say different kind of fish to frie.

Fiber, simple paper (news paper) fibre may be a solution, coconut dust and fibre or saw dust as well. I had considered Rice hulls as well. These particles and fibers will burn out during firing and obviously make the clay lighter and more porous. Don't be afraid of bursting, the clay pellets can handle it if normal low firing techniques are used. If you are low firing in a wood kiln, there is no problem at all, only electric and gas ovens may suffer from smoke development.

The lower you fire, (around 700-850 °C), the more porosity you'll get and keep. But here also it depends on the kind of clay. Use low firing clay only, no stoneware or any other clay that vitrifies over 1150° -1200 C. But you should anyway fire high enough to fix the clay. It should not desintegrate over time. Brick debries can be used as well - if you can get them for free at some brick factory or even a "brick village". But here again, be careful to not get underfired bricks, which are useless for the purpose. Drop them in water for a few days and crush tem with a hammer. If the debries get kinda loamy and "sticky" in your hands, the bricks were underfired. The debries should stay "crisp" and sandy instead.

    Bookmark   June 20, 2009 at 1:02AM
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One more thing hem_krish,

Balls, pellets or any round shapes are kinda time consuming to manufacture, as you need to roll them by hand. There is square shaped expanded clay around, and so can you use those as well.

It's much quicker to manufacture square shaped pellets. I have thought of a technique how to quickly manufacture them without use of machines or sofisticated tools, as well as through rather unskilled workers. If you want to know more about it (as I guess this is going to far at this place) just drop me an email:

Cheers, Jean-Luc

    Bookmark   June 21, 2009 at 12:22AM
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I would think that the terra cotta would work since some people even use pea gravel and river rock.

    Bookmark   June 22, 2009 at 8:33AM
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Could you not make the clay balls the same way people make seed balls in a rotating barrel? Would that take just way too long?

Why can we not put two consecutive replies without changing the subject line? That seems a little stupid.

    Bookmark   June 22, 2009 at 8:35AM
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"Could you not make the clay balls the same way people make seed balls in a rotating barrel? Would that take just way too long?"

Most probably the expanded clay balls are made in such a way. But clay behaves differently - it's kinda sticky. Here also we need a very specific technology. If you know the exact technology, have building plans for a bigger barrel and the whole enchilada that goes with it, you can always do that. But what may work, and be worth the effort for some small quantity (volume) of seed balls, may not be profitable for such clay balls. Also, you need to put the balls in fire prove (actually clay) boxes, before firing them, as you can't put them loose in a kiln!

Just think of what I said about square shaped pellets
My idea was to cut slices, then stripes, pack them when completely dried out together with other (wet) clay stripes, the way I get a kind of a brick (block). Those 'bricks' are stacked easily in a kiln - and only later when fired, you break them down to pellets. It does not actually matter if the size of such pellets (actually dices) is totally regular.

When thinking of a manufacturing process, you need to consider all aspects of the production ;-)

    Bookmark   June 22, 2009 at 11:49PM
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Hi jean-luc,
? Is your last plan for square "dices" going to use any ideal % of fiber mixed in with the low firing clay when it goes into the kiln ?

    Bookmark   June 23, 2009 at 6:15AM
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Hi gringojay
"? Is your last plan for square "dices" going to use any ideal % of fiber mixed in with the low firing clay when it goes into the kiln ?"

Ambas maneras son posibles.
You can do that either way. In case you use the described technique (strips, that are packed to a block when fired) long fibres (coco) may be inappropriate though. Well, because you need to break the dices from the stripes.

It seems unusual and perhaps hazardous, but it actually isn't. The fibres burn out long time before the clay transforms at a molecular level. Technically speaking you only use Bisque firing. At 800 - 950° C most clay has sintered, making it less fragile while still porous.

As for the concept of mixing fibres with the clay, my idea has actually derived from a material called paper clay also known and commercialized as "superclay". You may also read

I have had another thought in the meantime: in a next step the fired dices could be put in a rotating drum, containing water and Porcelaine balls (hand made an high fired stoneware balls would do the job as well). When only processed for about 1-2 hours, or even less - in such way, they would become smother and the edges would kinda sand off.

I have seen such 'low tech' rotating drums here in Thailand, made from 5 gallon (20L) water bottles. They are actually used to grind glaze mixes to a super fine level, but they seem perfectly appropriate for the purpose to me. Still, at this point we already think -and become kinda semi-industrialized ;-)

    Bookmark   June 24, 2009 at 2:15AM
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I've made a 3D sketch of how I see the way of piling up those clay stripes. In fact one can put those on top of normal bricks (in a artisanal kiln of course) to fire them. The lateral (x3) part is actually a simple (still soft) roll which is wrapped around the stack of stripes. It is only supposed to hold the stack together but it also helps to distribute heat all around and prevents bending of the stripes. This matters only if fired higher, or in case one uses additives to make the clay sinter at even lower temperatures (optional). 3D- 24/06/09

Top shows a clay slice cut into stripes - next shows how they are supposed to look wen piled up and "wrapped".
The thing looks a bit like a wood pile, - well that's what I was able to do in no time. Hope it illustrates the concept... ;-)

    Bookmark   June 24, 2009 at 11:17AM
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Hello everyone,

Forgive me for intrusion.

YOu may find the terra cotta technology for stoves to be most useful for making terra cotta as an alternative to hydroton.

I am an emerging potter and was working with clay stoves for sometime now. I was able to build clay stoves and was designing them to be light and highly insulating. I mix the clay with either saw dust or coco dust. That is true, the mix burns during firing in the kiln which provides the insulating effect for the stove. So far i was successful with the insulating effect but not yet with making the stove light. Mr. Rok Oblak, one of my mentors will be able to tell you more about producing highly porous clay mixes. He uses a combination of six parts of saw dust to one part of clay. Please visit YOu may also check the video clips of Mr. Larry Winiarski about making bricks for the rocket stove. He makes very light weight bricks that can float in water, meaning highly porous terra cotta balls should be very possible.

i hope these helps.

All the best


    Bookmark   August 4, 2011 at 6:52AM
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